Comment No, he can't declassify DoE stuff. (Score 1) 99
While you are broadly right, the Department of Energy has (AFAIK the only) classified materials that the President has no control over. Energy has "Restricted Data"–nuclear weapons information that's classified by law under the Atomic Energy Act, not merely deemed classified by the President under Executive Order 13526. Restricted Data can only legally be declassified by the DoE after thorough review, not by an Executive decree.
It's why the DoE has the legendary and totally misunderstood "Above Top Secret" Q clearance–you can have all the TS/SCI clearances you want, but by law you need the DoE's specific to see their secret stuff.